Sun Safety for Pale Dullards
You hate to see it. A large, red, peeling uncle proudly proclaiming that he’s “finally got his base tan.” A dude in a bucket hat slathering his face with SPF 90 goo at 6:30pm on a hot August night in New England. A porcelain-skinned redhead trusting a beach umbrella to protect her all day from the July Hawaiian sun. A freckle-faced woman apoplectic that her shoulders got burnt watching her Cleveland Indians for three hours on a partly cloudy April afternoon. A new mother, paranoid that her baby’s getting too much sunlight through his stroller canopy on a twenty-minute walk in the shade. A widely beloved professional football doofus suggesting that adequate hydration prevents sunburns.
You hate to see it, but you see it all the time! You see it all the time because general sun safety education in America is, bluntly, nonexistent. And that’s a shame! We’re the southernmost majority-white country in the Northern Hemisphere, and we can’t stop getting our dumb asses roasted — literally! — by something as routine and predictable as the friggin’ sun. Most embarrassingly, this trend comes in parallel with and in spite of a gradually replenishing ozone layer, a skyrocketing market share for sun protection clothing and products, increasing levels of overall education, and an at least theoretical increase in our collective awareness of the no good very bad things that unmitigated summer sunlight will do to our delicate, precious skin.
If we are smarter than ever before, and buying and using more things than ever before to protect us from annually decreasing amounts of ultraviolet radiation, and still turning bright red and skin-cancerous with alarming consistency, then probably we are gravely misunderstanding when and where and how the sun poses the most danger to us. And honestly, I don’t blame us! Take a look at this real dogshit advice, straight from the Environmental Protection Agency’s website:
I think this sucks ass! I think it also tracks perfectly with the prevailing national level of effort that goes toward UV avoidance — a mix of apathy, confusion, and misplaced caution. We can do so much better than this!
Look, full disclaimer, nobody — not even the scientists who study this shit for fun and/or a living— fully understands how tanning actually works. Any precise thresholds drawn between between things like UVA and UVB or “an okay amount of sun exposure” and “too much sun exposure” are artificial and arbitrary. It is impossible to accurately model exactly how much of the sun’s ultraviolet radiation will get reflected off of black asphalt and white sand and open water. But! There’s been enough research on these topics and others like them to provide we the laymen with some simple tools and concepts we can use to do our best. Let’s learn how to use these!
The UV Index
Bar none, this is the single most useful tool that we can use in order to avoid excessive ultraviolet light and all the nasty sunburns and premature aging that come with it. It is also frequently gravely misunderstood and poorly communicated because its derivation is all math-y.
What it is
The UV Index is, stated plainly, a weighted measurement of the rate at which sunburn-causing ultraviolet radiation reaches the surface of the earth. It is a simple linear scale, which means that twice as much sunburn-causing UV radiation reaches the surface of the earth every minute when the UV Index is 8 (200 mW/m²) as it does when the UV Index is 4 (100 mW/m²). But what does any of this actually mean?
What it means
All human skin can absorb some amount of ultraviolet radiation before crossing some admittedly arbitrary “damage” threshold. Pale white skin can handle much less energy than dark brown skin before burning, of course, which means that different people need to take different precautionary measures when they’re up against the same UV Index.
Here is a graphic from the National Oceanic and Atmospheric Administration that pretty adequately tells you everything you need to know:
Let’s say you are a “usually burns” type of person — like, hundred percent European white, but not quite Viking-Irish white white. The aforementioned UV Index of 4 means you will start to experience some level of skin damage after anywhere from 50 to 84 minutes in the sunlight. The aforementioned UV Index of 8 — which, again, means twice as much UV radiation hitting the earth per minute as when the UV Index is 4 — yeah, sure enough, look at that, you’ve got 25 to 42 minutes before you’re in trouble.
You will see on the infographic that skin that “usually burns” has a burn threshold of 30–50 mJ/cm², and who the hell has time to figure out standard units like these with all the UV rays coming in hot? An ugly but frankly vastly more useful metric for sunburn thresholds can be derived by multiplying the UV Index over the number of hours spent outside in the sun; let’s call this UVI-Hours. One UVI-Hour is 3600 UVI-Seconds, or 90000 mJ/m², or 9 mJ/cm². This means a person who “usually burns” has a sunburn threshold of 3.3 to 5.6 UVI-Hours — and we’ll call it four to keep things simple, dammit! So a burn will set in after: an hour at UV Index 4; thirty minutes at UV Index 8; twenty minutes at UV Index 12; fifteen minutes at UV Index 16; and so on. All the math is consistent, which might susprise you if you’re new to math. Welcome!
How we’re botching it
Now, sadly, here is the World Health Organization attempting to explain what the UV Index means for you in an infographic you’re far more likely to see than the NOAA’s very good and helpful one above.
This is, like EPA’s SunWise advice from above, pretty terrible! This doesn’t quantify anything at all for a pale dullard seeking even a remedial understanding of sun safety. It ignores that different skin types burn at drastically different rates, opting instead for blanket advice. For a UV Index of 8 here, we’re told to avoid the midday sun and that sunscreen and a hat are a must. And yet recall, the NOAA infographic suggests that even a “usually burns” person can safely stay outside for 25 to 42 minutes when the UV Index is 8. That’s not enough time for a day at the beach or a game at the ballpark, but it’s plenty of time to walk a mile or eat lunch at a picnic table without slathering on the sunscreen. On the other hand, note that for a UV Index of 2 we’re told by the WHO that we can safely stay outside with no protection. But… the math and the infographic say our “usually burns” friend might start to burn after just an hour and forty minutes when the UV Index is 2! Hell, an “always burns” person will be burnt after an hour and forty minutes at UV Index 2, and might start to burn after only half an hour. This WHO graphic can go straight to hell!
The Fitzpatrick Scale
Who’s ready to talk about melanin? Wait, no, come back. Sun safety is like, the one extra-sociological reason skin color matters.
What it is
The Fitzpatrick scale consists of six skin types ranging from Type I (the lightest) to Type VI (the darkest). It has been used and abused for everything from makeup marketing to hair removal protocols to diversifying emojis. But we are interested in it primarily as a better way to characterize skin sensitivities to UV rays than using terms like — what was it again? — Viking-Irish white-white.
What it means
Oh come on, you know damn well what it means! Type I skin is most susceptible to sunburn and Type VI skin is the least susceptible to sunburn. We’ve been over this!
The problem is, sources disagree over where to put the burn thresholds for different skin types. After scouring the Internet for research papers and UV protection app algorithms, I threw together the table on the left. It seems like no one can agree on just how red a patch of skin needs to turn before it’s considered sunburned, or on where to draw the line between various Fitzpatrick skin types. This is understandable — it’s not like skin comes in six discrete colors with six distinct qauntities of melanin, you know? In fact…
How we’re botching it
It’s just not the most consistent scale out there. Skin type is a hard thing to quantify and we do ourselves an added disservice when we try to measure it by way of correlated but decidedly different qualities like ethnic origin, hair color, and eye color.
Here, let’s check in with various classification tables and see if we can pin down what constitutes having Type III skin.
What a mess! The silver lining here is that with such an imprecise scale, and with so little agreement on how much UV radiation each skin type can safely withstand, you can pretty safely dismiss the entire concept beyond its ability to vaguely define your UVI-Hour burn threshold.
Sun Protection Factor (SPF)
Oh damn, I buried the lede. This is like, the single most commonly misunderstood element of sun safety, and the one most readily abused by people trying to make a buck or two off of the general public’s confusion.
What it is
The SPF (or UPF) of any material — glass windows, cotton shirts, zinc sunscreens, beach umbrellas — is the inverse of the relative amount of UV radiation that passes through it. That’s all it is! If you are wearing a layer of SPF 30 sunscreen, then 1/30 of the UV radiation that hits the layer of sunscreen will pass through it and get absorbed by your skin; the rest of the UV radiation will be reflected away or absorbed by the sunscreen. This effectively cuts the UV Index by a factor of 30 (hence: sun protection factor) or, if you prefer, it increases the time you can safely spend in the sun by a factor of 30. That’s pretty neat!
What it means
The graph on the left sums it up pretty well, I think, but to fully appreciate SPF we should combine it with our knowledge of the UV Index.
Let’s go back to our “usually burns” friend, the guy who can handle roughly four UV Index-hours. (He should probably classify his skin as Type II or III.) When the UV Index is 8, as it is in, say, Boston, on a midsummer’s midday, this means he will burn in half an hour. If he applies an SPF 30 sunscreen, however, he will be safe from the sun — and specifically, the sun at its peak, where it only remains for an hour or so — for fifteen hours. Thanks, sunscreen!
But now let’s consider a Type I individual on a Caribbean vacation where the UV Index is 12. With a burn threshold of just two UVI-Hours, this person’s going to get burnt in just ten minutes without any SPF. So she slathers on the same SPF 30 sunscreen, dutifully reapplies it all day, and… still gets a sunburn after three-hundred minutes, or five hours.
How we’re botching it
People just have a tendency to think linearly, especially when they don’t fully understand what numbers are measuring. When we hear blanket recommendations like “use a sunscren of at least SPF 30,” we tend to think an SPF as low as 5 or 10 is completely useless. But do you know what has an SPF of 5 or 10? A white cotton tee! Even an SPF as low as 2 is blocking out 50% of the sun’s UV rays. That’s doubling the amount of time you can spend in the sun, which is nothing to scoff at.
We also really ought to use and recognize the term SPF for materials beyond lotions and clothing. For instance — should you worry about getting a sunburn while you are driving? Only if you roll down your windows, really. The windshield’s got a built-in SPF of 50 and the passenger windows, made of regular glass, are somewhere around SPF 15. What if you are lying down under a tree, whose leaves seem to block out roughly three quarters of the sunlight? Well that’s essentially an SPF of 4, since just just 1/4 of the sun’s UV rays hit you through the trees. But we don’t talk about partial shade in these very specific and meaningful terms, opting instead to say things like “seek shade.”
Furthermore, SPF is not additive, but multiplicative. If you’re sitting under an SPF 15 beach umbrella and you’re covered in SPF 15 sunscreen, you’ve got an effective SPF of 225; just 6.67% of the UV rays are making it through the umbrella, and only 6.67% of those rays are making it to your skin, and so overall just 1/225 of the sun’s UV rays that made it through the ozone are actually hitting your skin. Congratulations, you are now UV invincible! Thanks to a mild sunscreen and a very shitty beach umbrella, you are immune to the fucking sun! (You are not.)
Just a Few More Things
- It’s worth noting and reiterating that the UV Index — the rate at which ultraviolet energy reaches the surface of the earth — has nothing to do with the temperature. (You can get a sunburn when you are freezing! You can also go into heat stroke when the UV Index is 2.) Instead it has everything to do with the local atmospheric conditions and the elevation angle of the sun above the horizon.
- Because the local atmospheric conditions vary hour by hour and day to day, it is wise to check the UV Index on a day-of basis rather than relying on extended forecasts. Meteorologists take into account both the cloud cover and the local ozone thickness when they predict the UV Index, and we all know that their track record at knowing where Wednesday’s clouds will be on Tuesday afternoon is, ah, hmm.
- The angle of the sun, on the other hand, is one hundred percent knowable and predictable for every location at every time of day for every day of the year. Understanding the “clear sky” daily and yearly UV Index curves for your neck of the woods is arguably more useful than understanding the temperature patterns, and it is inarguably easier to do.
- At sunrise and sunset, when the sun is very low on the horizon, the UV Index is infinitesimally small. Don’t be the doofus who puts sunscreen on his face at, like, 7:00pm in July, when the sun is five or ten degrees above the horizon. This is honestly the equivalent of putting on sunscreen in January in Iceland.
- A base tan has an SPF of about 2 or 3. What this means is that once you’re thoroughly tan, you can stay out in the sun two or three times as long without getting burned. (But how did you get thoroughly tan in the first place? You got repeatedly burned, you pale dullard you!)
- That said, a base tan does not change your overall skin type. You do not tan “from” Type II skin “into” Type III skin. You have the skin you have, and it burns and tans and suffers in the sun accordingly.
- Sunlight intensity peaks in the Northern Hemisphere on the summer solstice, on or around June 20. This means the UV Index is generally higher in late April than it is on Labor Day Weekend! If this runs completely counterintuitive to your understanding of the sun being at its strongest when the temperature is hottest, please reread the first bullet here a hundred times. I don’t know what to tell you!
- It’s important to remember that white sand and sea foam can reflect 20–25% of UV light right the hell into your thighs, face, whathaveyou. This is especially nasty because it’ll sneak right under a beach umbrella when you feel completely safe in the shade — take it from me!
- Snow can reflect 80% of UV light, effectively almost doubling the UV Index. Generally when there is snow on the ground, the UV Index will be low enough for this not to matter whatsoever, but then again, spring skiing exists.
- Just because a sunscreen is sold and marketed as “SPF 30” does not mean that merely spraying or rubbing it onto your skin will actually afford you an SPF of 30. The SPF of 30 might only be valid when the sunscreen is slathered on all gooey and thick-like, and the fact that they’re always telling you to reapply that stuff every hour or two should be a pretty big tell that it’s, you know, maybe not actually going to give you thirty times as long in the sun as your bare skin will.
- Lastly, this one is important. You cannot feel ultraviolet radiation. You cannot trust your senses to protect you from a sunburn at all. The warm-to-hot sensation you feel when you bask in direct sunlight is harmless thermal radiation. On the other hand, by the time you feel the pain from a sunburn, the damage was done several hours ago, and if you’re still in the sun at that point, oh boy are you fucked!
Putting It All Together
Look, we could spend all day talking about the details behind all this, but frankly, we’ve gone long enough already. You have all the tools you need now. There’s hope for you yet, pale dullard! Now go forth and stay safe in the sun this summer!
